Composition and method for blackening metal article surfaces



United States Patent US. Cl. 148-6.24 16 Claims ABSTRACT OF THE DISCLOSURE Compositions and baths for the surface blackening of ferrous metal comprising an alkali metal hydroxide, an alkali metal nitrate and/or an alkali metal nitrite, preferably both such nitrate and nitrite, and as a red smut inhibitor a phenylthiourea of the formula wherein R and R are hydrogen, phenyl or tolyl, and X is hydrogen or methyl, with the proviso that when R is hydrogen, R is hydrogen, phenyl or tolyl, and when R is phenyl or tolyl, R is hydrogen.

This invention reltaes to blackening of metal articles and more especially to a new and improved composition and method for producing black coatings on the surface of ferrous metal aticles.

The production of black coatings on ferrous metal articles heretofore by the use of conventional blackening baths, has been accompanied by the production of a red smut on the blackened metal surface. The smut has been due to the blackening bath being contaminated by red iron oxide and/or copper, with such contamination occurring during the use of the bath. Conventional blackening baths or solutions are comprised of a solution in water of a solid blackening composition containing an alkali metal hydroxide, an alkali metal nitrate and/or an alkali metal nitrite. The solid composition is mixed with water in sufiicient amount to produce a blackening solution having a boiling temperature between 255 F. and 325 F. The ferrous metal article or articles to be blackened are immersed in the bath while maintaining the boiling temperature of the bath for a time sufficient to produce the desired black coating on the article surface.

Heretofore thiourea per se and alkyl thioureas, for instance diethyl thiourea, have been added to the conventional blackening solutions or baths for the purpose of preventing the deposition of the smut on the ferrous metal surfaces and maintaining the blackening efliciency of the baths.

One object of this invention is to provide a new and improved composition for the surface blackening of ferrous metal articles.

Another object is to provide a composition for the surface blackening of ferrous metal articles characterized by an aqueous solution of the composition exhibiting a considerably improved blackening power over prior art surface blackening compositions.

Another object is to provide a composition for the surface blackening of ferrous metal articles characterized by an aqueous solution of the composition having a considerably longer life than prior art surface blackening compositions.

A further object is to provide a composition for the "ice surface blackening of ferrous metal articles, characterized by an aqueous solution of the composition exhibiting considerable less sedimentation of red rust than prior art surface blackening compositions.

A further object is to provide a new and improved method for blackening the surface or surfaces of ferrous metal articles.

In accordance with the present invention, we have found that the addition of an unsubstituted or substituted monoor di-phenyl thiourea to the prior or conventional blackening baths resulted in a considerably improved blackening bath or solution for blackening ferrous metal surfaces, over the prior or conventional blackening baths having added thereto an alkyl thiourea, such as diethyl thiourea, or thiourea per se, by reasons of (1) producing appreciably deeper and more uniform black smut-free coatings after considerable or extensive use of the bath for surface blackening than wa produced by the prior or conventional blackening baths; (2) having a materially longer life than the conventional blackening baths; (3) having an appreciable less rusty appearance after appreciable use of the bath for surface blackening than the prior or conventional blackening baths; (4) having appreciably smaller size rust particles suspended therein than the conventional baths after considerable or extensive use of the bath for surface blackening, which is important from the standpoint of obtaining smoother black coatings and less drag out of smut on the finished part; and (5) considerably less rust particles sedimenting out of the baths of this invention than sediment out of the prior or conveintional blackening baths. And it was entirely surprising and unexpected that the presence of the phenyl radical instead of the alkyl radical of the alkyl thiourea of the hydrogen atom of urea per se resulted in such improvements of the blackening compositions herein over the conventional blackening compositions or baths.

The blackening composition of this invention comprises a phenyl thiourea, an alkali metal hydroxide, an alkali metal nitrate and/or an alkali metal nitrite. The alkali metal moiety of the three last-mentioned compounds can be sodium or potassium. This blackening composition, which is a solid particulate mixture, is mixed with Water to provide the blackening bath or solution of this invention and preferably in the proportions of about 6%- 7% lbs. of the solid particulate mixture per gallon of total solution.

The phenylthiourea herein has the formula:

wherein 'R and R are each a hydrogen atom or an un substituted phenyl group or tolyl group, and X is a hydrogen atom or a methyl group, with the provision that when R is the hydrogen, R is either hydrogen or the phenyl or tolyl group, and when R, is the phenyl or tolyl group, R is hydrogen. The methyl of the tolyl group or groups is in the ortho or para position. Compounds included within such formula are monophenyl thiourea, N,N-di-phenylthiourea, N,N-diphenylthiourea, monotolylthiourea, N,N-diolylthiourea and N,N'-ditolylthiourea.

The phenylthiourea is added to the dry blackening composition herein or it may be added separately to the ultimate blackening bath, in a minor and effective amount, preferably in amount of about 0.022 parts by weight.

The dry blackening composition herein, which is a solid finely particulate or powder mixture, will then contain, by weight, about 0.02-2 parts of the phenyl thiourea, from 50-90 parst of the alkali metal hydroxide and from 1050 parts of each of the alkali metal nitrate and/or nitrite. This dry solid blackening composition is mixed together with water in preparing the blackening bath in such amounts as will bring the boiling point of the bath solution to within the temperature range of between 255 F. and 325 F.

Although we do not mean to be bound by theory, it appears that the action of the phenyl thiourea smut inhibitor herein is to maintain the fine rust particles dispersed in the bath as fine particles and without any substantial agglomeration of the rust particles to form larger size particles, with the result the rust particles will not cause a red smut to be formed on the ferrous metal surface. Consequently the blackened surface of the ferrous metal article when Withdrawn from the blackening bath is a smut-free or substantially smut-free black sur- Example I Comparative tests were made on the effect of adding to separate conventional blackening baths thiourea per se and diethyl-thiourea of the prior art, monophenyl thiourea of the present invention, and no additive. The blackening bath for each test was made by admixing with water 7 /4, lbs. of the following dry powder blackening composition per gallon of total solution.

Parts by wt. NaOH 65 NaNO NaNoz 2.84 grams per gallon of each of the thiourea per se, diethyl thiourea, and monophenyl thiourea were added to the separate blackening bath, for the particular test, prepared as aforesaid, and one blackening bath prepared as aforesaid had nothing added to it.

All baths were maintained at approximately 290 F. during the blackening by addition of deionized water, which also maintained the volume of the baths. Equal amounts of steel wool were suspended in all baths to artificially age them. Panels of steel of dimensions of 4" length, 2%" width and 0.010" thickness were immersed in the baths maintained at about 290 F. Prior to immersing the panels in the baths, all panels were activated by immersing them in aqueous hydrochloric acid of 37 weight percent acid concentration. One panel was immersed in each blackening bath. The test results obtained are set forth in the following table.

The quality of the black on the ferrous metal panel changed very little 'with use of the blackening bath having monophenyl thiourea added to it, and was still good after 16 hours use of the bath. However, when no additive was added to the blackening bath and when thiourea per se was added thereto, the quality of the black on the ferrous metal panels deteriorated considerably with usage of the bath from an initial good quality black, and was a poor quality black in each case after 16 hours use of the bath. With diethyl-thiourea as the additive, the quality of the black of the ferrous metal panels deteriorated appreciably with use of the bath for surface blackening from an initial good quality, i.e. a uniform deep black, to a fair quality black, which is a black characterized by having a greyish overtone to the black, after 16 hours. The poor quality black of the foregoing table means a black which has no depth of color owing to lack of continuity of the coating. Further, as shown by the table of test results, the appearance of the blackening bath of this invention containing the added monophenyl thiourea showed only a light rust and was an orange-red color after aging as contrasted with the baths containing the diethyl thiourea and thiourea of the prior art which showed moderate and considerable rust respectively and were each a rusty red in color. The prior art or conventional blackening bath containing no additive showed considerable rust in big lumps, and was also a rusty red in color. Further, a blackening bath of this invention containing the monophenyl thiourea showed a relatively small amount of sedimentation, designated in the foregoing Table I of test results as 1, whereas the prior art bath containing diethyl thiourea showed an amount of sedimentation about twice as great and the prior art bath containing thiourea per se showed an amount of sedimentation about ten times as great, designated in Table I as respectively 2 and 10. The black ening bath containing no additive also showed an amount of sedimentation about ten times as great as the blackening bath of this invention, also designated in Table I as 10. By Sedimentation as used in the foregoing table of test results is meant the settling out from the bath of solid particulate matter, largely iron oxides and hydrated oxides, and is determined by loss of light transmission through the solution.

tension, so as to reduce caustic spray without thereby producing an excessive volume of foam, and also to reduce bumping. The Naxonate G is a tradename sodium xylene snlfonate of low chloride content which functions as a wetting agent, and serves to enable articles immersed in the blackening bath to be more easily rinsed of the TABLE Thiourea Diethyl Monophenyl N o Additive per se thiourea thiourea Black after aging P Appgisrance 01 solution after oor Poor Fair Good. Cglilisiderable rust Considerable rust Moderate rust.. Light rust.

gbig lumps. Color of solution after aging... Red Red Red Sedimentation 10 10 2 1Orange-Red.

blackening solution upon removal of the articles from the bath. The above formulation of Example II and the formulations of Examples III-1X hereafter are dry solid powder compositions and are preferably mixed with water to form the blackening bath in the proportions of about 6%-7% lbs. of such dry powder per gallon of total solution.

Example III Parts by wt. NaOH 54.5 NaNO 23.0 NaNO 22.0 Monophenyl thiourea 0.5 Naxonate G 0.01

Example IV NaOH 64.5 NaNO 22.0 NaNO 13.0 Sodium aluminate 0.3 N,N-diphenylthiourea 0.2 Naxonate G 0.01

Example V NaOH 64.5 NaNO 22.0 NaNO 13.0 N,N-diphenylthiourea 0.5 Naxonate G 0.01

Example VI NaOH 54.5 NaNO 23.0 NaNO 22.0 N,N-diphenylthiourea 0.5 Naxonate G 0.01

Example VII NaOH 54.5 NaNO 22.0 NaNO 22.0 Sodium aluminate 0.3 N,N diphenylthiourea 0.2 Naxonate G 0.01

Example VIII NaOH 64.5 NaNO 22.0 NaNO 13.0 2,2 dimethyl N,N-diphenylthiourea 0.5 Naxonate G 0.01

Example IX NaOH 54.5 NaNO 23.0 NaNO 22.0 Sodium aluminate 0.3 2,2 dimethyl N,N diphenylthiourea 0.2 Naxonate G 0.01

2 wherein R and R are each from the group consisting of hydrogen, phenyl and tolyl, and X is from the group consisting of hydrogen and methyl, with the provision that when R is hydrogen, R is from the group consisting of hydrogen, phenyl and tolyl, and when R is from the group consisting of phenyl and tolyl, R is hydrogen, from 50-90 parts of an alkali metal hydroxide, from 10-50 parts of an alkali metal nitrate, and from 10-50 parts of an alkali metal nitrite.

2. The composition of claim 1 wherein the phenylthiourea is monophenylthiourea.

3. The composition of claim 1 wherein the phenylthiourea is N,N-diphenylthiourea.

4. The composition of claim 1 wherein the phenylthiourea is N,N'-diphenylthiourea.

5. A blackening bath for surface blackening of ferrous metal articles consisting essentially of an aqueous solution, by weight, from about 0.02-2 parts of a phenylthiourea of the formula wherein R and R are each from the group consisting of hydrogen, phenyl and tolyl, and X is from the group consisting of hydrogen and methyl, with the provision that when R, is hydrogen, R is from the group consisting of hydrogen, phenyl and tolyl, and when R is from the group consisting of phenyl and tolyl, R is hydrogen, from 50-90 parts of an alkali metal hydroxide, from 10- 50 parts of an alkali metal nitrate, and from 10-50 parts of an alkali metal nitrite.

6. The bath of claim 5 wherein the phenylthiourea is monophenylthiourea.

7. The bath of claim 5 wherein is N,N-diphenylthioruea.

8. The bath of claim 5 wherein the phenyl thiourea is N,N-diphenylthioruea.

9. The bath of claim 5 having been prepared by mixing with water a dry solid blackening composition in the proportions of about 6%-7% lbs. of the dry solid composition per gallon of total solution, the dry solid composition consisting essentially of the phenyl thiourea, alkali metal hydroxide, alkali metal nitrate and alkali metal nitrile within the weight ranges specified in clam 5'.

10. A process for surface blackening ferrous metal articles which comprises immersing the ferrous metal article in a blackening bath consisting essentially of aqueous solution, a blackening composition mixture of, by weight,

from about 0.02-2 parts of a phenylthiourea of the formula the phenylthioruea is wherein R and R are each from the group consisting of hydrogen, phenyl and tolyl, and X is from the group consisting of hydrogen and methyl, with the provision that when R is hydrogen, R is from the group consisting of hydrogen, phenyl and tolyl, and when R is from the group consisting of phenyl and tolyl, R is hydrogen, from 50-90 parts of an alkali metal hydroxide, from 10- 50 parts of an alkali metal nitrate, and from 10-50 parts of an alkal metal nitrite, said bath being prepared by admixing the blackening composition mixture with water in suflicient amount to bring the boiling point of the solution to a temperature within the temperature range of between 255 F. and 325 F., maintaining the article immersed in the bath while maintaining the boiling temperature of the bath solution for a time suificient to obtain a black coating on the article surface, and separating the black-coated article from the bath.

11. The process of claim 10 wherein the phenylthiourea is monophenylthiourea.

12. The process of claim 10 wherein the phenylthiourea is N,N-diphenylthiourea.

13. The process of claim 10 wherein the phenylthiourea is N,N'-dipheuyl thiourea.

14. In a dry solid composition for the surface blackening of ferrous metal articles comprising a mixture of, by weight, from 50-90 parts of an alkali metal hydroxide, from 10-50 parts of each of at least one material selected from the group consisting of an alkali metal nitrate and an alkali metal nitrite, and a thiourea, the improvement which comprises utilizing as the thiourea a phenylthiourea of the formula XQ-N wherein R and R are each from the group consisting of hydrogen, phenyl and tolyl, and X is from the group consisting of hydrogen and methyl, with the provision that when R is hydrogen, R is from the group consisting of hydrogen, phenyl and tolyl, and when R is from the group consisting of phenyl and tolyl, R is hydrogen, the phenylthiourea being present therein in a minor amount sufiicient to prevent the formation of red smut by an ultimate blackening bath on the ferrous metal surface.

15. The solid composition of claim 14 characterized by containing 'both the alkali metal nitrate and the alkali metal nitrite.

16. In a blackening bath for the surface blackening of ferrous metal articles comprising in aqueous solution, a blackening composition mixture of, by weight, from 50- 90 parts of an alkali metal hydroxide, from 10-50 parts of an alkali metal nitrate, from 1050 parts of an alkali metal nitrite, and a thiourea, the bath having been prepared by admixing the blackening composition mixture with water in suificient amount to bring the boiling point of the solution to a temperature within the temperature range of between 255 F. and 325 F., the improvement which comprises utilizing as the thiourea a phenylthiourea of the formula wherein R and R are each from the group consisting of hydrogen, phenyl and tolyl, and X is from the group consisting of hydrogen and methyl, with the provision that when R is hydrogen, R is from the group consisting of hydrogen, phenyl and tolyl, and when R is from the group consisting of phenyl and tolyl, R is hydrogen, the phenylthiourea being present therein in a minor amount suflicient to prevent the formation of a red smut on the ferrous metal surface.

References Cited UNITED STATES PATENTS UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 447 974 Dated June 3 F 1969 Inventor(s) Edward B. Saubestre and Juan liaidu It is certified that error appears in the above-identified" patent and that said Letters Patent are hereby corrected as shown below:

r- Column 1, line 31, "reltaes" should read relates Column 2, line 34, "of" (first occurrence) should read or line 60, "the" should be deleted; line 66 "N,Ndiolylthiourea should read "N,N-ditolylthiourea Column 3, line 4, "parst" should read parts line 61, "table" should read Table Column 4, line 58, "tradename" should read tradenamed Column 6, line 14, "an" should read in line 45, "nitrile" should read nitrite line 48, an should be inserted after "of" and before "aqueous".

SIGNED AND SEALED our 2 1 1969 m Am Edward M. mm, 11-.

WHLIAM E- 'SGHUYm, IB- Auestmg Officer Commissioner of Patents 

